Process for increasing the wall thickness in hollow sections

ABSTRACT

The invention relates to a process for producing a region of greater wall thickness in a longitudinal hollow section ( 1 ) which, to this end, is subjected to a radial and axial pressure and plastically deformed thereby. The hollow section ( 1 ) is secured in a matrix ( 2 ) corresponding to the section dimensions which has an enlarged cross section corresponding to the intended final dimensions of the hollow section ( 1 ) in the deformation region. The essential embodiment consists in that the deformation to attain an increased wall thickness ( 14 ) takes place in a region between the ends of the section. In addition, the wall thickness ( 19 ) can be increased at at least one of the ends of the section.

The invention relates to a process for production of an area ofincreased wall thickness in a longitudinal section and to a device forapplication of the process.

A process such as this for production of increased wall thickness hasbeen disclosed in SU-A-1417954, FIG. 1. In the process a longitudinalhollow section is secured in a die matching the external dimensions ofthe die, is subjected to axial pressure by an axial piston applyingpressure on both sides, and in addition the profile cavity is subjectedto radial pressure by a suitable medium. A hollow section is produced asa result, one which undergoes reduction of the internal cross-sectionover the entire length so that increased wall thickness is obtained.

German patent application 44 37 395 A1 describes a process for shaping apipe end in which the pipe to be shaped is subjected to internal andexternal axial pressure, the pipe being secured in a die correspondingto the exterior dimensions of the pipe, and in the end area of the pipeto be shaped the die also being provided with a shape matching the finaldimensions of the pipe after the shaping process and the pipe beingsubjected in the area to be shaped to end pressure by at least one axialpiston and at the same time to radial pressure by a fluid.

The practice of shaping hollow sections by axial pressure and by radialpressure applied simultaneously by means of a fluid is known under thedesignation “internal high pressure shaping” (see DE-A 29 35 086, EP 0484 789 B1). Such a process does not involve increase in the wallthickness in the hollow section shaped; what results is rather reductionin the thickness of the remaining wall by extension of the material. Aprocess for upsetting section ends by plastic deformation by means of astepped axial piston is disclosed in U.S. Pat. No. 5,203,194.Introduction of additional radial pressure by means of a fluid is notprovided in this process.

Patent application DE 44 37 395 A1 is concerned primarily with plasticdeformation of pipe ends for the manufacture of optimized-mass andlong-lived exhaust systems for internal combustion engines. Areas ofsuch subassemblies with cross-sectional dimensions modified on the basisof function serve the purpose, for example, of fastening special machineelements or subassemblies. Such subassemblies and machine elements maybe represented, among other things, by sound absorbers, catalysts, orfitting flanges.

The object of Patent Application DE 44 37 395 A1 is development of aprocess for upsetting pipe ends and a device for application of theprocess by means of which a tubular element having generally optimumcross-sectional dimensions may be provided with end sections havinglarger cross-sectional dimensions so that the internal diameter remainsunchanged, virtually free of a transitional area, even in the area ofthe pipe end, and yet the cross-sectional dimensions required remainavailable for the joining of additional components, by welding forexample.

The object of the invention is to increase the shaping options of thestate-of-the-art process as described in the preamble of Claim 1 inorder to produce an area of increased wall thickness in an oblong hollowsection. Modification of the internal cross-section of the hollowsection is not to take place in the process.

The solution claimed for the invention is to be seen from thedescriptive portion of Claim 1 and is based on a procedure as specifiedin the preamble of Claim 1.

By application of this process more or less minor tool modificationsneed be made to provide any given area between section ends withincreased wall thickness rather than the entire length of a hollowsection, the internal cross-section remaining the same. The hollowsection itself may be of any desired cross-sectional shape (e.g.,rectangular, as specified in U.S. Pat. No. 5,203,194, round, polygonal,open or closed, etc). The only requirement for this purpose is that diesor axial pistons have the same shape.

In addition, the hollow section may consist both of a metallic and anonmetallic material (such as a plastic).

The areas situated between the ends of a section and also the sectionends may be upset and provided with increased wall thickness in theconcomitant plastic deformation.

The invention is described in what follows with reference to exemplaryembodiments, and with supplementary reference made to the explanationspresented in Patent Application DE 44 37 395 A1. The accompanyingdrawing shows

in FIG. 1 a device into which a hollow section to be shaped has beenintroduced, with an axial piston in an initial and final position,

in FIG. 2 a modified device with two axial pistons mounted opposite eachother in initial and final positions, and

in FIG. 3 an additionally modified device, in this instance as well withtwo axial pistons mounted opposite each other and two hollow sectionareas to be deformed.

FIG. 1 shows a hollow section 1, such as a steel pipe, introduced into adivided hollow die 2 whose parting plane 3 extends orthogonally to theplane of the drawing intersecting with the longitudinal axis of thehollow section 1. The hollow section 1 extends into the cavity 10 of thehollow die 2 until the face of the section rests on the bottom 5.

Approximately in the central area of the hollow section 1 the dividedhollow die 2 has a circumferential cross-sectional extension, so that agap 6 is formed between the outer wall of the hollow section 1 and theinterior diameter of the hollow die 2, which is extended in this area.The transition from the smaller to the larger diameter is in the form ofa retaining edge 7 positioned at an angle of approximately 30° to theperpendicular to the longitudinal axis 4.

The tool set also includes an axial piston 8 which is provided with athrough axial bore 9 for a fluid. Water, preferably water with syntheticadditives, for example, is suitable as pressurized fluid.

The shaped axial piston 8 consists of a front piston component 8.1 whichis to be introduced into the hollow section 1 and is suitably adapted inthe shaping process, adjoining which component is a rear pistoncomponent 8.2 adapted to the dimensions of the cavity 10. The transitionfrom the smaller to the larger cross-section of the axial piston 8 isdesigned as a sealing shoulder whose plane of section inclines slightly(for example, at an angle of 15°) to the perpendicular to thelongitudinal axis 4 of the axial piston 8.

In the area of the gap 6 in the hollow die 2 the axial piston 8 has anumber (six, for example) of rows of radially arranged bores 13 whichextend from the axial bore 9 to the peripheral surface of the axialpiston 8. Each row of bores is situated in a plane perpendicular to theplane of the drawing and consists of a number (six, for example) ofuniformly spaced individual bores (which incline, for example, at anangle of 60°).

After the sealing shoulder 12 of the axial piston 8 comes to restagainst the face of the hollow section 1 (the end of the front pistoncomponent 8.1 is situated more or less in the area of the frontretaining edge 7 of the gap 6), the piston is first subjected to anaxial force F_(A) (5 kN, for example). Fluid is then pumped through theaxial bore 9 through the axial piston 8 and subsequently subjected to acertain pressure (for example, 0.5 MPa). In this situation there isformed between the face of the axial piston 8 and the bottom of thehollow die 2 a forced seating area (cavity 10) in which the hollowsection 1 resting against the wall of the die is supported againstbuckling. In addition, the fluid is applied by way of the radial bores 9to the area of the hollow section 1 to be upset. With increase in theaxial force F_(A) applied to the axial piston 8 (e.g., to a valueexceeding 100 kN), accompanied by simultaneous increase in the internalpressure P_(i) of the fluid (e.g., to at least 15 MPa), plasticdeformation of the hollow section 1 takes place in the area to be shapedto the point of complete filling of the gap 6. The interiorcross-section of the wall-thickened area 14 of the hollow section 1 (cf.the lower part of FIG. 1) remains unchanged, but the wall of this areais thickened, for example, by three millimeters.

After the deformation process has been completed, the axial piston isremoved from the divided hollow die 2 and the pressure of the fluid issimultaneously removed. After the sections of the die have beenseparated the shaped hollow section 1 may be removed and then ifnecessary undergo additional working (such as bending, joining to othercomponents, etc.).

Consequently, in the process claimed for the invention an upsettingprocess is applied to thicken the wall of a hollow section 1 in aparticular area. Application of a tangential load to the wall of thehollow section also takes place in the course of the extension processintroduced as a result of the radial load applied by the fluid, and atthe same as a result of axial load application by the force of the axialpiston 8. The resulting multidimensional load application overcomes theresistance to elastic deformation to a specific extent and leads to theplastic deformation desired.

It is useful for the axial force F_(A) to increase, together with theinterior pressure P_(i), as a function of the open cross-sectional areaA_(R), in accordance with the statement

F _(A)=1.1×A _(R) ×P _(i).

This ensures among other things that in no circumstances will thesection wall buckle on one side in the forced seating area as a resultof increase in the axial forces on one side. At the same time it ensuressealing by the sealing shoulder 12 and the face of the hollow section 1.

The face of the hollow section 1 forming a sealing pair with the sealingshoulder 12 of the axial piston 8 is produced as a surface ensuringsealing and axial loading capacity by metal removing, cold working,mechanical, or thermal separation processes.

It is conceivable that the radial bores 9 could if necessary bedispensed with, inasmuch as the existing dimensioning tolerance betweenthe front part of the piston 8.1 and the interior wall of the hollowsection 1, along with the concomitant specific escape of pressurebuildup by the fluid, and accordingly the radial load application to thehollow section 1 in the area of the gap 6, is already ensured.

FIG. 2 illustrates a modified embodiment of the tool employed toincrease the wall thickness in the central area of the hollow section 1.For the most part reference may be made to the preceding commentsregarding the exemplary embodiment shown in FIG. 1, for which reason thesame reference numbers are used in the appropriate places in subsequentdiscussion.

In this exemplary embodiment as well use is made of a divided die 15whose plane of separation extends along the longitudinal axis 4. Unlikethe exemplary embodiment shown in FIG. 1, two axial pistons 16 are usedhere, each consisting of a front piston element 16.1 and a rear pistonelement 16.2. During shaping, that is, the upsetting process carried outto fill the gap 16 with the material of the hollow section 1, the twoaxial pistons 16 may be moved toward each other (under the action offorce F_(A)), the pressure of a fluid P_(i) being applied at the sametime. It is also conceivable, however, that only one of the two axialpistons 16 will move, while the other serves exclusively to seal thesystem (sealing shoulder 12) and to support the material of the hollowsection in the area of the retaining edge 7.

The exemplary embodiment illustrated in FIG. 3 also involves operationwith two axial pistons 16, 17, which move in a divided die 18 in thisinstance as well. In contrast to the exemplary embodiment shown in FIG.2, not only is a wall-thickened area 14 now produced between the ends(that is, in the central area, for example) of the hollow section 1, buta wall-thickened area 19 is additionally formed at one of the two endsof the section (the right one). This wall-thickened area could, ofcourse, be formed at the opposite end of the section, or even at bothends.

The divided die 18 is for this purpose provided in the area of thesection end in question with a corresponding cross-sectional extension,with the result of creation of another gap 20 which later, afterdeformation, is filled with the material of the hollow section 1.

In order that initially the gap 6 and only then the gap 20 will befilled with the material of the hollow section 1 (the inverse sequenceis conceivable) during movement of the two axial pistons 16, 17 (or eventhe movement of only one of the two pistons) in the context of theextrusion process, it is useful to treat the material of the hollowsection 1 in the area of the gap 6 selectively so that it ultimatelybecomes more “deformation compliant” than is the case in the area of thegap 20. This can be accomplished, for example, by applyingfriction-reducing coatings to the tool (die 18 and/or axial piston 16,17) and/or to the hollow section 1. This effect can also be achieved,for example, by local heating (through heating ducts 22 mounted in thedivided die 18, extending over the length of the gap 6, and enclosingthe hollow section 1. In temperature control account must of course betaken of the boiling point of the fluid (water, for example), so thatthis measure is of limited effectiveness, especially if the hollowsection 1 is made of a metallic material. Another option would be toprovide the hollow section 1 in the area of the gap 6 in advance with asomewhat smaller wall thickness or to anneal it (in the case of a metalhollow section), and so render it more “deformation compliant” than isthe case in the area of the gap 20, that is, at the end of the profilealso to be shaped. Such measures could also prove to be useful ifincreased wall thickness is to be imparted to at least two areas of thehollow section 1 situated between the ends of the section and noincrease in wall thickness has been provided at the end of the sectionitself.

What is claimed is:
 1. A process for reshaping the exterior profile of aworkpiece having a longitudinal bore therethrough, comprising: providinga die having a cavity with a wall conforming to said exterior profile ofsaid workpiece and at least one enlarged section disposed between andspaced from ends of said cavity and cooperable with the remainingportion of said cavity wall to provide a selected exterior profile ofsaid workpiece; inserting said workpiece into said cavity; inserting atleast one ram member into said cavity, having a first section providedwith an external profile conforming to the interior profile of saidworkpiece receivable within an end of said workpiece, a second sectionprovided with an external profile conforming to said exterior profile ofsaid workpiece, a shoulder disposed between said first and secondsections engageable with an end of said workpiece, and a fluidpassageway interconnecting an inlet port and at least one outlet portdisposed on said first section, registrable with said enlarged sectionof said cavity wall when said ram member is inserted into said cavitywith said first section thereof inserted into said workpiece and saidshoulder engages said end of said workpiece; and simultaneously applyinga longitudinal force on said ram member and a fluid under pressure tosaid passageway, causing said workpiece to deform and thus flow intosaid enlarged section of said cavity wall to form said selected exteriorprofile of said workpiece while maintaining said interior profilethereof.
 2. The process according to claim 1 including heating saidworkpiece to enhance its flowability.
 3. The process according to claim1 wherein said enlarged section of said cavity wall is positioned sothat the enlarged wall section of said workpiece formed lies between theends of said workpiece.
 4. The process according to claim 1 includingapplying a lubricant to the exterior surface of said workpiece.
 5. Theprocess of claim 1 including providing at least a second enlargedsection of said cavity wall disposed between the ends of said first ramsection when said first ram section is inserted into said workpiece andsaid shoulder engages said end of said workpiece.
 6. The process ofclaim 1 wherein said workpiece is tubular and said enlarged section ofsaid cavity is annular.
 7. The process according to claim 6 wherein saidpassageway includes an axially disposed section and at least oneradially disposed section communicating with said outlet port.
 8. Theprocess according to claim 1 wherein said die cavity has an open end anda closed end and wherein said passageway of said ram member communicateswith a second outlet port communicating with a chamber defined by aportion of said workpiece, an end wall of said cavity and an end wall ofsaid ram member when said workpiece is inserted in said cavity and saidfirst section of said ram member is inserted in said workpiece.
 9. Theprocess according to claim 1 wherein said die cavity includes two openends and including inserting the first sections of two of said rammembers through said open ends with the shoulders of said ram membersengaging ends of said workpiece.
 10. An apparatus for reshaping theexterior profile of a workpiece having a longitudinal bore therethrough,comprising: a die having a cavity with a wall conforming to saidexterior profile of said workpiece and at least one enlarged sectiondisposed between and spaced from ends of said cavity and cooperable withthe remaining portion of said cavity wall to provide a selected exteriorof said workpiece; at least one ram member insertable into said cavity,having a first section provided with an exterior profile conforming tothe interior profile of said workpiece, insertable into said bore ofsaid workpiece, a second section provided with an exterior profileconforming to said exterior profile of said workpiece, a shoulderdisposed between said first and second ram sections and a fluidpassageway having an inlet port communicable with a source of fluidunder pressure and at least one outlet port registrable with saidenlarged section of said cavity wall when said workpiece is insertedinto said cavity and said ram member is inserted in said cavity withsaid first ram section received in said workpiece and said shoulder ofsaid ram member engages an end of said workpiece; and means for applyinga longitudinally directed force on said ram member whereby upon saidworkpiece being inserted in said cavity, said ram member being insertedinto said cavity with said first ram section being inserted into saidworkpiece and said shoulder of said ram member engaging an end of saidworkpiece, and fluid under pressure being applied to said passageway,said workpiece shall be caused to deform with a portion thereof flowinginto said enlarged section of said cavity wall to provide said selectedexterior profile of said workpiece.
 11. An apparatus according to claim10 including means for heating at least a portion of said workpiece whendisposed within said cavity.
 12. An apparatus according to claim 10wherein said ram sections are cylindrical and said enlarged section isannular.
 13. An apparatus according to claim 10 wherein said cavityincludes an open end and a closed end, and said first ram sectionincludes a second outlet port intercommunicating said passageway and achamber defined by an end wall of said cavity, a portion of the interiorwall of said workpiece and an end wall of said first ram section whensaid workpiece and ram member are inserted in said cavity.
 14. Anapparatus according to claim 10 wherein said cavity includes twoopenings, and including two ram members each insertable through one ofsaid cavity openings.
 15. An apparatus according to claim 10 whereinsaid die is formed of two sections mated together along a plane passingthrough a longitudinal center line thereof.